I was gonna respond earlier but I forgot, it's not very hard or tedious to do through notepad, make a copy of the replay you wanna edit and start editing (playing) from the frame you want.
After you finished editing what you wanted, save it and open it in another notepad.
Then copy the variables of the frames you edited and replace them with the variables of the original replay in the corresponding frames.

Its easier to show through video so if you need any help add me on discord rox#6840